Packaging machinery

ABSTRACT

A vertical form, fill and seal (VFFS) packaging machine comprising a pair of sealing jaws ( 12; 100; 200,202; 302,304 ) mounted directly or indirectly on parallel shafts ( 10; 102; 206,208; 300 ) for rotation in opposite directions on opposite sides of the path of the packaging material ( 36; 118; 204; 308 ) so that the jaws engage the packaging material simultaneously on opposite sides to form successive horizontal seals, and stripping means comprising, in association with the sealing jaw on each side of the path of the packaging material, a pair of stripper carriers ( 22; 54; 66; 116; 222,224,226,228; 314 ) mounted for rotation around the corresponding shaft at or near the respective ends thereof, or about an axis parallel to the shaft, a horizontal stripper bar ( 18 B;  40 A;  50 A;  62; 110; 234; 310 ) mounted at its respective ends on the two stripper carriers and arranged to be movable with respect to the stripper carriers so that the stripper bar can engage the packaging film along a predetermined vertical stripping path along which, in cooperation with a similar stripper bar associated with the sealing jaw on the other side of the packaging material, it acts to displace downwards any product which might otherwise be trapped in the area of the seal, the stripper carriers being arranged to be rotated faster than the shafts at least while the stripper bars are performing each stripping operation.

[0001] This invention is concerned particularly with packaging machinescommonly referred to as vertical form fill and seal (VFFS) machines. Itwill be described specifically with reference to such machines, but itshould be understood that at least certain aspects of this invention areapplicable to machines in which the packaging material moves obliquelydownwards or even horizontally while bags are being formed. All suchmachines are encompassed in this context by the expression “machines ofthe type described”.

[0002] In a VFFS machine, a web of packaging material is drawn along aformer and then passes downwards in tubular formation; the edges aresealed longitudinally as the packaging material moves downwards(assuming, as is preferred, that the packaging material movescontinuously), after which horizontal seals are made at regularintervals to form individual bags. A measured quantity of product to bepackaged is dropped into each bag before a top seal is formed by sealingjaws which simultaneously form the bottom seal of the next bag. Thesealing jaws commonly include a cutting device which separatessuccessive bags.

[0003] With some materials and in some circumstances, it is desirable toprovide a stripping device to ensure that each measured quantity of theproduct passes downwards reliably into its bag before the top seal isformed. Examples of stripping devices are described in European patentNo. 165819 and U.S. Pat. Nos. 2,915,866, 3,070,931, 3,256,673 and3,262,244. A further example of a stripping device is described in ourpatent application WO96/32328. The present invention is concernedparticularly with new forms of stripping devices for packaging machinesof this general type.

[0004] According to one aspect of this invention, a packaging machine ofthe type described, for forming downwardly moving packaging materialinto bags containing product, comprises a pair of sealing jaws mounteddirectly or indirectly on parallel shafts for rotation in oppositedirections on opposite sides of the path of the packaging material sothat the jaws engage the packaging material simultaneously on oppositesides to form successive horizontal seals (or alternate seals if thereare, for example, two jaws on each shaft), and stripping meanscomprising, in association with the sealing jaw on each side of the pathof the packaging material, a pair of stripper carriers mounted forrotation around the corresponding shaft at or near the respective endsthereof, or about an axis parallel to the shaft, a horizontal stripperbar mounted at its respective ends on the two stripper carriers andarranged to be movable with respect to the stripper carriers so that thestripper bar can engage the packaging film along a predeterminedvertical stripping path along which, in cooperation with a similarstripper bar associated with the sealing jaw on the other side of thepackaging material, it acts to displace downwards any product whichmight otherwise be trapped in the area of the seal, the strippercarriers being arranged to be rotated faster than the shafts at leastwhile the stripper bars are performing each stripping operation.

[0005] The stripper carriers are preferably driven by a servo motorseparate from the motor driving the shafts, which latter motor may alsobe a servo motor. In this context by “servo motor” we mean a motor ofwhich the output shaft is electronically timed and controlled as to itsspeed. By this means, the stripper bars can be arranged to be drivenfaster than the sealing jaws while performing each stripping operation;however, if the number of stripper bars equals the number of sealingjaws, for example, then the average speed of the stripper bars wouldequal that of the sealing jaws. It should be noted, however, that thesealing jaws may be driven at a cyclically varying speed in order toproduce the required bag length which may vary for different products;accordingly, as mentioned above, what is important is that the stripperbars should move faster than the sealing jaws so as to overtake themwhile performing each stripping operation, whatever the speed of thesealing jaws happens to be.

[0006] The speed of the jaws, while creating each seal, would normallybe equal to the speed of the packaging material which may also bevariable as a result of being driven by yet another servo motor.

[0007] Instead of the stripper bars being driven by an independent servomotor, they may receive their drive from the motor driving the sealingjaws, for example via a gear train or other mechanism whereby the speedof the stripper bars is arranged to fluctuate cyclically, for examplesinusoidally or approximately so, with respect to the speed of the jaws.By this means, a stripper bar could overtake the corresponding sealingjaw to perform each stripping operation, and then slow down to allow thejaw to overtake it in preparation for the next stripping operation. Thismodification, which constitutes an altenative aspect of this invention,may also be applied to belt or chain mounted stripper bars as describedin our patent application WO96/32328.

[0008] Alternatively, a common servo motor may be used to drive thesealing jaws and the strippers if, for example, there are two pairs ofsealing jaws with a single stripper (on each side of the packagingmaterial) which is driven at a speed exactly twice that of the sealingjaws.

[0009] Each stripper bar may be pivotally mounted on its correspondingstripper carriers so that the part of the stripper bar which contactsthe packaging material during each stripping operation can movevertically through a predetermined distance, in contact with thepackaging material, while overtaking the jaw and performing eachstripping operation. One or more springs may be provided to urge thestripper bar into contact with the packaging material with a controlledforce. Alternatively, each stripper bar may be controlled as to itsangular position with respect to the stripper carriers by means of oneor more cams. Another possibility is that each stripper bar may bemounted on its stripper carriers via leaf springs.

[0010] According to another aspect of this invention, a packagingmachine of the type described comprises a pair of cooperating sealingdevices mounted directly or indirectly on parallel shafts for rotationin opposite directions on opposite sides of the path of the packagingmaterial so that the sealing devices engage the packaging materialsimultaneously on opposite sides to form successive horizontal seals,each sealing device comprising two oppositely disposed sealing jawswhereby two seals are formed during each revolution of the shaft; andstripping means comprising a pair of cooperating stripper bars forengaging opposite sides of the packaging material, each stripper barbeing carried at its ends by arms which are pivotally or otherwisemovably mounted on rotary stripper carrying members lying beyond theends of the sealing jaws and being driven at an average or set speedtwice that of the shaft, whereby the stripping means strips downwardsany product lying within the packaging material, in each region about tobe sealed, in advance of each pair of sealing jaws engaging thepackaging material, the pivotal or other movement of the arms being suchas to allow the stripper bars to move past the sealing jaws in order toperform the stripping operations.

[0011] The shaft is preferably driven by a servo motor capable ofvarying the shaft speed as may be necessary, for example in order toform bags of different lengths. The stripper carriers may be driven by aseparate servo motor at an average speed twice that of the shaft; oralternatively, the stripper carriers may be driven by the servo motordriving the shaft but via a transmission which doubles the speed of thestripper carriers relative to the shaft.

[0012] The arms carrying each stripper bar may be pivotally mounted onthe respective stripper carriers or may alternatively be telescopicallymounted so as to slide in a linear bearing or other guide in order toenable the stripper bar to move to different distances from the axis ofrotation of the stripper carriers. In either case, the stripper bar ispreferably urged outwards by one or more springs, but may alternativelybe controlled as to its position by a cam slideway.

[0013] According to another aspect of this invention a packaging machineof the type described comprises one or more (preferably a pair) ofsealing devices arranged to engage opposite sides of the packagingmaterial tube to produce transverse seals at regular intervals, eachsealing device being continuously driven for movement along a closedpath; and a pair of stripping devices arranged to engage opposite sidesof the packaging material tube to strip downwards any product containedwithin the tube in the area about to be sealed by the sealing devices;each stripping device comprising a stripper bar carried at its ends byarms which are movably mounted on stripper carriers located near theends of the corresponding sealing device, whereby movement of the armsrelative to the stripper carriers causes or allows each bar to moveoutwards away from the axis of rotation so as to clear and thus be ableto move past the corresponding sealing device so as to perform astripping operation in advance of engagement of the sealing device withthe packaging material, the stripper carrier being driven at arotational speed such as to cause the stripper to have a speed greaterthan the sealing device at least while passing the sealing device andperforming a stripping operation.

[0014] Examples of different forms of machine according to thisinvention are shown diagrammatically in the accompanying drawings. Inthese drawings:

[0015]FIG. 1 is a partly sectioned view of part of one machine;

[0016] FIGS. 2 to 4 are diagrammatic representations of three differentforms of machine;

[0017] FIGS. 5 to 8 are diagrammatic representations of anotherdifferent form of machine at different stages in its operation;

[0018]FIG. 9 is a plan view of another different machine;

[0019]FIG. 10 is a fragmentary side view of the machine shown in FIG. 9;

[0020]FIGS. 11 and 12 show details of the machine shown in FIG. 9; and

[0021]FIG. 13 is a diagrammatic representation of another differentmachine.

[0022]FIG. 1 shows in section the parts located at one end of a shaft 10carrying a pair of oppositely disposed sealing jaws 12 of which outersurfaces 12A will cooperate with a similar sealing jaw arrangement onthe other side of the downwardly moving packaging material (not shownhere, but see FIG. 2) to perform horizontal sealing operations on thepackaging material. The jaws may also, as is common, include cooperatingcutting arrangements for cutting the packaging material horizontallyalong the mid-region of each seal so as to simultaneously separate thebags.

[0023] The shaft 10 is mounted at one end in bearings 14 in a side frame16. The other end of the shaft is similarly mounted in another sideframe. In the region of that other side frame the mechanism may bevirtually an exact mirror image of the arrangement shown in FIG. 1.

[0024] Two oppositely disposed stripper members 18 and 20 are pivotallymounted at each end (only one end being shown in FIG. 1) on a strippercarrier 22 which is mounted on a sleeve 24 rotatable around the shaft 10with the aid of a bearing 26. Each stripper member has an inner endportion 18A, 20A which is parallel to the axis of the shaft 10 and isrotatable in the member 22.

[0025] As shown in connection with the stripper member 18, the activeportion 18B, comprises a bar parallel to the axis of the shaft 10, thisportion of the stripper being arranged to engage the packaging materialand to perform stripping operations in cooperation with a similarstripping member on the other side of the packaging material. A spring26 for urging the stripping member against the packaging material isshown diagrammatically in FIG. 1 in relation to the stripping member 18,the same arrangement being provided for the stripping member 20.

[0026] One end of the sleeve 24 adjacent to the side frame 16 carries agear 24A which meshes with a gear 28 fixed to a shaft 30 which isparallel to the shaft 10 and is rotatable in a bearing 32 in the sideframe 16. At its outer end the shaft 30 carries a pulley 32 which isdriven by a timing belt 34 passing also around a pulley on a drive shaft(not shown) which extends across the machine (parallel to the shaft 10)so as to drive the stripper carrier at the other end of the shaft 10 inthe same way. As will be understood, the shaft driving the belt 34 ispreferably, as mentioned above, driven by a servo motor separate fromthe motor (preferably also a servo motor) driving the shaft 10.

[0027] In place of the belt 34 and pulley 32 it is possible to use achain and sprocket arrangement.

[0028]FIG. 2 shows diagrammatically an arrangement similar to FIG. 1,viewed in the direction of the axis of the shaft 10. It shows theapparatus at the stage of forming a horizontal seal across packagingmaterial 36 to complete one bag 38 while forming the bottom sealed edgeof the next bag. The jaws 12 at this stage extend horizontally, and itwill be understood that there is a similar piece of apparatus on theother side of the packaging material 36. Thus the jaws, which areheated, cooperate to form each horizontal seal.

[0029]FIG. 2 shows only one stripping member 40 which is pivoted at 42to the radially extending stripper carrier 22. The spring 26 is shownanchored at one end to the stripper carrier 22 and at the other end tothe stripping member so as to urge the stripping member in a clockwisedirection about the pivot 42. Thus the horizontal bar portion of thestripping member (corresponding to the part 18B in FIG. 1) is pressedagainst the packaging material. It will be understood that, shortlybefore the stage shown in FIG. 2, the stripping member lagged behind thejaw 12, and that its greater speed resulted in it overtaking the jaw 12while performing a stripping operation in cooperation with a similarstripping member on the other side of the packaging material.

[0030] When the stripping member is away from the packaging material, itis free to rotate about the pivot 42, relative to the stripper carrier22, to the position shown in chain dotted outline 40 ¹ under theinfluence of the spring 26.

[0031] As shown also in FIG. 2, each sealing jaw may carry a pivotedclamp 42 (only one of which is shown complete, albeit diagrammatically)pivotally mounted at 44 on the jaw. A spring 46 acting between the jawand the clamp normally, while the clamp is remote from the packagingmaterial, holds the clamp against a stop 48. When the outer end of theclamp (which also comprises a horizontal bar extending right across thepackaging material similarly to the stripper member) engages thepackaging material and cooperates with a similar clamp on the other sideof the packaging material, it swings against the action of the spring toapproximately the position shown in chain dotted outline 42A.

[0032] The purpose of the clamps is to prevent product from droppinginto the region of the seal just as the seal is about to be formed.

[0033]FIG. 2 shows, for convenience, only one stripper member. Inpractice there may be two diametrically opposite to one another forcooperating with the respective jaws 12, as shown in FIG. 1. Preferably,however, the arrangement operates with only one stripper driven aboutthe axis of the shaft 10 at twice the speed (or an average of twice) ofthe shaft 10. Another possibility is that there could be, for example,three strippers spaced apart by 120° about the axis of the shaft 10; inthat case the member 24 carrying the strippers would rotate at anaverage speed equal to two thirds that of the shaft 10, though again thestrippers would need to move faster than the jaws while performing eachstripping operation. Other possibilities are, for example, that therecould be three or four equally spaced sealing jaws on each shaft, with asimilar or smaller number of strippers.

[0034] It will be understood that the speed and timing with which thestripper members approach the packaging material should be such thattheir horizontal bar portions reach the packaging material (above theregion of the forthcoming seal) and move along it, past the clamp andjaw, before both the clamp and the jaw reach the packaging material.With that objective, the outmost positions of the clamps (set by thestop 48 in the example shown in FIG. 2) need to be determinedaccordingly.

[0035] The stripping and clamping bars are parallel to the shaft axes,as described above, and are preferably straight Alternatively, either orboth may be slightly outwardly bowed so as to ensure adequate contactpressure against the packaging material in their middle regions.

[0036] The clamps, by, virtue of their geometry (including their pivotpositions), may move upwards relative to the packaging material whenthey first contact the packaging material and thus perform a slightupward stripping action.

[0037]FIGS. 3 and 4 show further alternatives. FIG. 3 shows anarrangement in which the or each stripper member 50 is pivotally mountedat 52 to a carrier 54 on a member 56 rotating with respect to the shaft10. However, instead of the horizontal bar portion 50A of the strippermember being urged towards the packaging material by a spring, in thisexample it is controlled by a cam. Specifically, in the example shown,the inner end of the stripper member carries a roller 58 which runs in agroove-like cam track 60 which may be formed in or mounted on the sideframe 16 shown in FIG. 1. As before, a similar arrangement exists at theother end of the shaft 10.

[0038]FIG. 4 shows an alternative arrangement in which the or eachstripper member 62 is mounted at its opposite ends via leaf springs 64and screws 65 so as to be resiliently movable relative to a strippercarrier 66; each leaf spring may be straight when in the unstressedstate, and flexes (as shown) while urging the stripper member againstthe packaging material. Also, in this example, each jaw carries a clamp68 which is similarly mounted at its opposite ends via leaf springs 70;the inner end of each leaf spring is secured by one or more screws 72 toa projection 74 on the corresponding jaw.

[0039] With each of the above-described arrangements, the stripper driveis preferably independent of that for the sealing jaw or jaws. Moreover,each arrangement may be so constructed that the drive to the stripperscan be stopped in the event of a product being packed which does notcall for stripping. If, as mentioned above, the stripper drive isderived from the motor driving the jaws, the drive to the stripper orstrippers can also be stopped by means of a clutch when necessary.

[0040] The arrangements described above are based on sealing jaws movingwith a purely rotary motion. Alternatively, each sealing jaw may bemounted on the shaft 10 via an arrangement which allows or causes thejaw to remain in a fixed orientation at least while it is engaging thepackaging material, which condition may occur along a predetermineddistance, rather than instantaneously as in the case of a purely rotarysealing jaw. Such sealing jaws are commonly referred to as D-motion jawsbecause the locus of each jaw is D-shaped.

[0041] FIGS. 5 to 8 show diagrammatically different stages in therotation of a different form of machine according to this invention.

[0042] The machine comprises a sealing device 100 which includesoppositely disposed sealing jaws 100A and 100B and is rotatable about anaxis 102. Associated with each of the sealing jaws is a horizontalproduct clamping roller or bar 104, only one of which is shown. Theclamping roller is parallel to the axis 102 and extends beyond both endsof the sealing device 100, being carried at its respective ends by twoarms 106 pivotally mounted on the sealing device by pins 108.

[0043] A stripper bar 110 is likewise carried at its respective ends byarms 112 which are pivoted by pins 114 to respective stripper carrierswhich are shown diagrammatically as arms 116. The arms 116 rotate aboutthe axis 102 at twice the speed of the sealing device 100.

[0044] FIGS. 5 to 9 show the sealing and stripping arrangement on oneside of a downwardly moving flattened tube of packaging material 118. Itwill be understood that a similar sealing and stripping arrangement isprovided on the left-hand side of the packaging material 118, so thatthe stripper bars and clamping rollers on opposite sides of thepackaging material co-operate with one another to perform the requiredstripping and clamping functions, and likewise the sealing jaws onopposite sides of the packaging material co-operate to producehorizontal seals at regular intervals along the packaging material. Thesealing jaws also include cutting means 100C for cutting the packagingfilm horizontally so as to separate the successively formed filled bags.

[0045] It will be understood that the stripper bar and the clampingroller are urged towards the packaging material by suitable springs (notshown).

[0046]FIG. 5 shows the arrangement at a stage shortly after the stripperbar 110 has begun to move along the packaging material so as to stripdownwards any product contained within the packaging material in thatarea. Shortly before this stage, the stripper bar, while-in a furtherextended position under the urging of the spring or springs, (with astop 112A engaging the arm 116) was able to pass the clamping roller 104(shown in its limiting outward position) and also the sealing jaw 100Awhich is about to make a seal.

[0047]FIG. 6 shows the arrangement after 20° of further rotation of thesealing member 100 and 40° of further rotation of the stripper. At thisstage, the clamping rollers 104 on opposite sides of the packagingmaterial begin to cooperate to prevent any product falling downwardspast them and into the region about to be sealed.

[0048]FIG. 7 shows the positions after 100 of further rotation of thesealing device and 20° of the stripper. Beyond this stage, there is noneed for the stripper bars to engage the packaging material, and it isindeed undesirable for them to do so as they might damage the product inthe just-formed bag. Each is accordingly guided away from the packagingmaterial by a stationary cam 120. The arrangement is showndiagrammatically, and in practice each arm 112 would carry a followerroller or wheel arranged to run along the corresponding cam. Acontinuation of the cam may be provided to control the return of thestripper to its outermost position in preparation for its next strippingoperation in association, this time, with the sealing jaw 100B.

[0049]FIG. 8 shows the arrangement at the completion of sealing, namelyafter 20° of further rotation of the sealing device and 40° of thestripper.

[0050] In the arrangement shown in FIGS. 5 to 8, the strippers may bedriven at a set speed twice that of the sealing device, but arepreferably driven by a servo motor so as to be capable of varying inspeed, the average speed still being twice that of the sealing device.

[0051] The speed at which the packaging material 118 is driven downwardsduring bag formation is not necessarily constant. It may be variedcyclically as a result of being driven by a separate servo motor inorder to optimise the machine operation. For example, the packagingmaterial may be of a type which needs to be slowed down during sealingin order to achieve an adequate jaw contact (sealing) time, differentpackaging materials requiring different sealing times; moreover, thespeed pattern between successive sealing operations needs to take intoaccount the required bag length. At the stage shown by FIG. 7, thevelocity of the packaging material may be increased so as to be greaterthan the downward velocity of the clamping rollers 104. This may beachieved by modulating the speed of the servo motor driving the weband/or by modulating the speed of the servo motor driving the sealingdevice.

[0052] FIGS. 9 to 12 show an arrangement which is similar in principleto that shown in FIGS. 5 to 8.

[0053]FIG. 9 is a partly sectioned plan view and shows the two sealingdevices 200 and 202 lying on opposite sides of a flattened tube ofpackaging material 204. The sealing devices are mounted respectively onshafts 206 and 208 carried by side frame members 210 and 212. A servomotor (not shown) drives the shafts in opposite directions and at equalspeeds. For this purpose a double-sided timing belt (not shown) connectsa pulley 214 on the shaft 206 with a similar pulley (not shown) on ashaft driven by the servo motor and with a pulley 216 (half the diameterof the other pulleys) on a further shaft 218. A gear 220 on the shaft206 meshes with a similar gear 221 on the shaft 208.

[0054] Carrier members for the stripper bars are in the form of gears222 and 224 for one stripper bar, and gears 226 and 228 for the otherstripper bar. These gears are all identical; gears 222 and 226 mesh withone another, and likewise gears 224 and 228. Each of these gears isrotatably mounted by means of a bearing around one end of one of theshafts 206, 208. A gear 230 on the shaft 218 (of the same diameter asthe gears 222,226 etc) meshes with the stripper-carrying gear 222, and asimilar gear (not shown) on the shaft 218 meshes with the gear 224 so asto drive the stripper-carrying gears at twice the speed of the shafts.206 and 208.

[0055]FIG. 10 shows some detail associated with one of thestripper-carrying gears 222. It shows one of the stripper-carrying arms232 which supports and drives one end of a stripper bar 234. The arm 232is pivoted to the gear 222 on a pin 236 and is urged in ananti-clockwise direction about the pin 236 by a spring 238 which pullsthe adjacent part of the arm 232 against a stop 240. Opposite ends ofthe spring 238 are anchored respectively to a pin 242 on the gear 230and to a screw 244 on the arm 232.

[0056] It will be understood therefore that FIG. 10 shows the stripperbar 234 in its outermost position. At this radius from the axis ofrotation 246 of the gear, it can pass the corresponding sealing jaws andclamping rollers prior to performing a stripping operation inco-operation with a similar stripping bar (not shown) carried by thegear 226. On engaging the packaging material 204, each stripper rotatesabout its pivot 236, against the action of the spring 238, as will beunderstood by reference to the example shown in FIGS. 5 to 8.

[0057] It is necessary to ensure alignment of the cooperating stripperbars as they move downwards along the packaging material. For thatpurpose, each stripper bar carries, at each end, a fixed gear segment248 (see FIG. 11) which meshes with a similar gear segment on theopposing stripper bar.

[0058] At each end of each of the shafts 206,208 (FIG. 9) there is aclamping roller carrying arrangement comprising a member 250 which isclamped to the shaft and which carries two pivoted arms 252 (see FIG.12) supporting the ends of the clamping rollers 254. The clampingrollers may in fact comprise rods each of which is surrounded by arotatable sleeve serving as a roller for engaging the packaging materialin a rolling manner.

[0059]FIG. 12 shows the arrangement of one of the members 250 with theassociated pivoted arms 252. The member 250 has a slot 256 which isclosed by a clamping screw 258 to clamp the member 250 on the shaft 208(in this example). Each arm 252 is pivoted to the member 250 by a pin260 and has an eye 262 at one end (opposite to the clamping rod 254) forengagement by one end of a tension spring 263 of which the other end issecured to a screw 264.

[0060] At the end which supports the clamping roller, each arm 252carries a fixed gear segment 266 for engaging a corresponding gearsegment on the opposed clamping roller arrangement to ensureregistration, as in the case of the stripper bars.

[0061] The phase relationship of the clamping rollers with respect tothe sealing jaws can be adjusted slightly by undoing the clamping screws258, rotating the members 250 about the shafts, and then tightening thescrews 258. Also, and more importantly, the phase relationship of thestripper bars with respect to the sealing jaws can be adjusted withinthe drive transmission to the stripper carrier gears. Alternatively, itwill be understood that the stripper carrier gears may be driven by aseparate servo motor; this would enable the speed pattern (including therotational phase) of the strippers to be varied independently of thesealing jaws, though the average speed of the strippers would still betwice that of the shafts carrying the sealing jaws.

[0062]FIG. 13 shows diagrammatically another different form of machineaccording to this invention. A shaft 300 carries two sealing jaws 302and 304 spaced apart by 180°, each carrying a pivotally mounted clampingroller 306 and including cutting means 307. A mirror-image arrangement(not shown) lies on the opposite side of a vertically moving flattenedtube of packaging material 308.

[0063] A single stripper bar 310 is mounted at its ends on two rods 312which are telescopically (slidably) carried by stripper carriers 314which are rotatable about the axis of the shaft 300 and are driven attwice the speed of the shaft 300 or at an average of twice the speed ifthe stripper carriers are driven by an independent servo motor. A spring316 urges the stripper bar outwards, its limiting outward position (asshown) being determined by stops 318 on the rods 312.

[0064]FIG. 13 shows the arrangement as the stripper bar 310 is about tocontact the packaging material and then perform a stripping operation(in cooperation with the stripper bar on the other side of the packagingmaterial) while passing the clamping roller and the sealer. The clampingrollers will reach the packaging material shortly after the area whichthey contact has been stripped by the stripper bars, which area is thusensured to be product free.

[0065] As in the previous two examples, the stripper bars may, shortlyafter passing the sealers, be displaced from the packaging material bystationary cams.

[0066] As an alternative to the gear segments 248 for maintainingregistration of the stripper bars, the following arrangement may beprovided: recessed portions of the stripper bars, at or near the ends ofthe bars, are arranged to engage and slide along two vertical rods. Thatis to say, the cooperating stripper bars, in the regions of their ends,slide along opposite sides of the two rods which thus ensure that thestripper bars remain in register with one another while performing eachstripping operation. A similar provision may be made for the clampingmembers.

1. A packaging machine of the type described, for forming downwardlymoving packaging material into bags containing product, comprising apair of sealing jaws (12; 100; 200,202; 302,304) mounted directly orindirectly on parallel shafts (10; 102; 206,208; 300) for rotation inopposite directions on opposite sides of the path of the packagingmaterial (36; 118; 204; 308) so that the jaws engage the packagingmaterial simultaneously on opposite sides to form successive horizontalseals, and stripping means comprising, in association with the sealingjaw on each side of the path of the packaging material, a pair ofstripper carriers (22; 54; 66; 116; 222,224,226,228; 314) mounted forrotation around the corresponding shaft at or near the respective endsthereof, or about an axis parallel to the shaft, a horizontal stripperbar (18B; 40A; 50A; 62; 110; 234; 310) mounted at its respective ends onthe two stripper carriers and arranged to be movable with respect to thestripper carriers so that the stripper bar can engage the packaging filmalong a predetermined vertical stripping path along which, incooperation with a similar stripper bar associated with the sealing jawon the other side of the packaging material, it acts to displacedownwards any product which might otherwise be trapped in the area ofthe seal, the stripper carriers being arranged to be rotated faster thanthe shafts at least while the stripper bars are performing eachstripping operation.
 2. A machine according to claim 1, in which themovable mounting of each stripper bar on its respective carriers causesor enables the stripper bar to move outwards from its axis of rotationand thus, owing to its greater speed, to overtake the correspondingsealing jar as it approaches the packaging material in preparation forperforming a stripping operation.
 3. A machine according to claim 2, inwhich each sealing jaw carries behind it a movably mounted clampingmember (42; 68; 104; 254) arranged, in cooperation with an opposedclamping member on the other side of the packaging material, to preventproduct from falling past it and into the area which is about to besealed or has just been sealed by the cooperating opposed sealing jaws,and in which each stripper bar is arranged by virtue of its speed andposition to pass the corresponding clamping member and to engage thepackaging material to commence a stripping operation before the clampingmember reaches the packaging material, thereby stripping also the areaabout to be engaged by the clamping member.
 4. A machine according toany one of claims 1 to 3, in which each shaft carries two sealing jaws180 degrees apart from one another, and the stripper carriers on eachside of the packaging material carry just one stripper bar and aredriven at a speed or average speed twice that of the shafts.
 5. Amachine according to any one of claims 1 to 4, in which the shafts aredriven by a servo motor and the stripper carriers are driven by aseparate servo motor.
 6. A machine according to claim 5, in which theservo motor driving the stripper carriers is controllable as to itsspeed and/or phase, whereby the stripping operation with respect to itsspeed and/or timing can be adjusted while the machine is running.
 7. Amachine according to any one of claims 1 to 6, in which each stripperbar is mounted at its ends on arms which are pivotally or slidablymounted on the corresponding stripper carriers.
 8. A packaging machineof the type described, comprising a pair of cooperating sealing devices(100; 200,202; 302,304) mounted directly or indirectly on parallelshafts (10; 102; 206,208; 300) for rotation in opposite directions onopposite sides of the path of the packaging material (36; 118; 204; 308)so that the sealing devices engage the packaging material simultaneouslyon opposite sides to form successive horizontal seals, each sealingdevice comprising two oppositely disposed sealing jaws (100A, 100B forexample) whereby two seals are formed during each revolution of theshafts; and stripping means comprising a pair of cooperating stripperbars (40A; 50A; 62; 110: 234; 310) for engaging opposite sides of thepackaging material, each stripper bar being carried at its ends by armswhich are pivotally or otherwise movably mounted on rotary strippercarrying members (22; 54; 66; 116; 222; 314) lying beyond the ends ofthe sealing jaws and being driven at an average or set speed twice thatof the shaft, whereby the stripping means strips downwards any productlying within the packaging material, in each region about to be sealed,in advance of each pair of sealing jaws engaging the packaging material,the pivotal or other movement of the arms being such as to allow thestripper bars to move past the sealing jaws in order to perform thestripping operations.
 9. A machine according to claim 8, in which eachsealing jaw carries behind it a movably mounted clamping member (42; 68;104; 254) arranged to engage the packaging material above the sealingjaw, the corresponding stripper bar being arranged to overtake theclamping member before performing each stripping operation.
 10. Apackaging machine of the type described, comprising one or more ofsealing devices (12; 100; 200,202) arranged to engage opposite sides ofthe packaging material (36; 118; 204) to produce transverse seals atregular intervals, each sealing device being continuously driven formovement along a closed path; and a pair of stripping devices arrangedto engage opposite sides of the packaging material to strip downwardsany product contained within the packaging material in the area about tobe sealed by the sealing devices; each stripping device comprising astripper bar (18B; 40A; 50A; 62; 110; 234) carried at its ends by arms(40; 50; 64; 112; 232) which are movably mounted on stripper carriers(22; 54; 66; 116; 222,224,226,228) located to the sides and separatelyfrom the corresponding sealing device, whereby movement of the armsrelative to the stripper carriers causes or allows each bar to move awayfrom the axis of rotation so as to clear and thus be able to move pastthe corresponding sealing device so as to perform a stripping operationin advance of engagement of the sealing device with the packagingmaterial, the stripper carriers being driven at a rotational speed suchas to cause the stripper to have a speed greater than the sealing deviceat least while passing the sealing device and performing a strippingoperation.
 11. A packaging machine of the type described, comprising twocooperating sealing devices each comprising at least one sealing jaw(100A, 100B for example) driven by a shaft (for example 102) so as tomove continuously along a closed path, and each sealing device having anassociated stripping means comprising at least one stripper bar (forexample 110) pivotally or otherwise movably mounted at its ends on tworotating carrier members (116) arranged to be driven continuously at aspeed which is greater than that of the shaft at least while performingeach stripping operation, the movable mounting of the stripper bar onthe corresponding carrier members allowing or causing the stripper barto move along a closed path extending around the path of the sealing jawor jaws and having a straight portion extending along the packagingmaterial to perform successive stripping operations in cooperation witha similarly movable stripper bar on the other side of the packagingmaterial.
 12. A machine according to claim 11, in which each sealingdevice comprises two oppositely disposed sealing jaws (100A and 100B forexample) and in which the stripping means associated with each sealingmeans comprises a single stripper bar (110) which is driven by thecarrier members (116) at a set or average speed twice that of the shaft(102) of the associated sealing means.
 13. A machine according to claim12, including means (238) for resiliently urging the stripper bar awayfrom the axis of rotation of the corresponding carrier members, wherebythe stripper bar lies at a large enough radius to be able to overtakeeach sealing jaw in preparation for performing a stripping operation.14. A machine according to claim 13, including means (120) for guidingthe stripper bar away from the packaging material after the completionof each stripping operation.
 15. A machine according to any one ofclaims 11 to 14, in which the carrier members (116) for each stripperbar (110) are mounted on end portions of the shaft of the correspondingsealing device for rotation relative to the shaft.